When detecting faults in main bearings of the cylinder block, it is important to minimize detection errors that could result in the part being incorrectly accepted or incorrectly rejected. Incorrect rejection of a cylinder block main bearing to the left and right of the tolerance limit will result in the need to replace the cylinder block. Incorrect acceptance of the support according to the smallest size may result in a loose cap-to-support fit and possible breakage. Incorrect acceptance of the support according to the largest size can lead to a gap between the liners and their subsequent play and rotation. In order to reduce the occurrence probability of the mentioned errors during the tolerance control, the authors estimated incorrectly accepted and incorrectly rejected main bearings during detecting faults with the use of inside calipers: NI 100-160 0.01; NI-PT160-0.001; NIC-PT 160-0.002. Twenty cylinder blocks were analyzed, in each of them five main bearings were subjected to control. It is calculated that at the repair program of 1000 YaMZ engines per year the use of NI-PT160-0.001 allows to reduce losses from incorrect rejection in 2.13 times and losses from incorrect acceptance in 1.88 times as compared with the use of NI 100-160 0.01. The use of NIC-PT 160-0.002 is irrational because of the possibility of increasing losses (discreteness of counting is twice coarser than the order of the measured value). The proposed methodology can be applied in detecting faults in other engine parts: for example, in checking the inner diameter of the cylinder liner and the big end of the connecting rod.